Scientists develop revolutionary nanotechnology copper solder

Oct 25, 2012

(Phys.org)—Scientists in the Advanced Materials and Nanosystems directorate at the Lockheed Martin Space Systems Advanced Technology Center (ATC) in Palo Alto have developed a revolutionary nanotechnology copper-based electrical interconnect material, or solder, that can be processed around 200 °C. Once fully optimized, the CuantumFuse solder material is expected to produce joints with up to 10 times the electrical and thermal conductivity compared to tin-based materials currently in use. Applications in military and commercial systems are currently under consideration.

"We are enormously excited about our CuantumFuse breakthrough, and are very pleased with the progress we're making to bring it to full maturity," said Dr. Kenneth Washington, vice president of the ATC. "We pride ourselves on providing innovations like CuantumFuse for space and defense applications, but in this case we are excited about the enormous potential of CuantumFuse in defense and commercial manufacturing applications."

In the past, nearly all solders contained lead, but there is now an urgent need for lead-free solder because of a worldwide effort to phase out hazardous materials in electronics. The European Union implemented lead-free solder in 2006. The State of California did so on January 1, 2007, followed soon thereafter by New Jersey and New York City.

The principal lead-free replacement – a combination of tin, silver and copper (Sn/Ag/Cu) – has proven acceptable to the consumer electronics industry that deals mostly with short product life cycles and relatively benign operating environments. However, multiple issues have arisen: high processing temperatures drive higher cost, the high tin content can lead to tin whiskers that can cause short circuits, and fractures are common in challenging environments, making it difficult to quantify reliability. These reliability concerns are particularly acute in systems for the military, aerospace, medical, oil and gas, and automotive industries. In such applications, long service life and robustness of components are critical, where vibration, shock, thermal cycling, humidity, and extreme temperature use can be common.

"To address these concerns, we realized a fundamentally new approach was needed to solve the lead-free solder challenge," said Dr. Alfred Zinn, materials scientist at the ATC and inventor of CuantumFuse solder. "Rather than finding another multi-component alloy, our team devised a solution based on the well-known melting point depression of materials in nanoparticle form. Given this nanoscale phenomenon, we've produced a solder paste based on pure copper."

A number of requirements were addressed in the development of the CuantumFuse solder paste including, but not limited to: 1) sufficiently small nanoparticle size, 2) a reasonable size distribution, 3) reaction scalability, 4) low cost synthesis, 5) oxidation and growth resistance at ambient conditions, and 6) robust particle fusion when subjected to elevated temperature. Copper was chosen because it is already used throughout the electronics industry as a trace, interconnect, and pad material, minimizing compatibility issues. It is cheap (1/4th the cost of tin; 1/100th the cost of silver, and 1/10,000th that of gold), abundant, and has 10 times the electrical and thermal conductivity compared to commercial tin-based solder.

The ATC has demonstrated CuantumFuse with the assembly of a small test camera board. "These accomplishments are extremely exciting and promising, but we still have to solve a number of technical challenges before CuantumFuse will be ready for routine use in military and commercial applications," said Mike Beck, director of the Advanced Materials and Nanosystems group at the ATC. "Solving these challenges, such as improving bond strength, is the focus on the group's ongoing research and development."

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User comments : 9

Great news for us techies! It has been clear lead free solder leaves something to be desired in several respects. It doesn't flow as well as the older lead based solder for one thing. It also takes a higher temperature to melt.

I look forward to using this new solder that melts at 200 degrees C or 392 degrees F.

I'm assuming that once the solder is fused, the melting point returns to that of pure copper. This could make rework and de-soldering problematic if not impossible, and could be a poor choice for hobbyists and prototyping.

I'm assuming that once the solder is fused, the melting point returns to that of pure copper. This could make rework and de-soldering problematic if not impossible, and could be a poor choice for hobbyists and prototyping.

It could be that on cooling the stuff ends up a chaotic mix of Cu crystals and half melted nano particles, as they are having problems with "bond strength." Sounds like this solder could be on the brittle side.

It's interesting approach, but the nanoparticle copper would be very prone to oxidation and its mechanical properties will not be probably very excellent too. It's merely a sealant or cement than solder. The main problem is, the common solder dissolves the underlying metal under formation of solid solution with it - this is how the reliability of soldering connection is achieved. The nanocopper solder would probably form build a sufficiently strong connections with itself, but its adhesion to another metallic surfaces will remain poor.

ValeriaT- Three common metal joining techniques- soldering, brazing and welding. If you cross section each of the three you will find that soldering does not dissolve the underlying material. The base metal(s) are wetted by the solder but there is a clearly delineated boundary. In brazing (sort of high temperature soldering) there is a transition area where an alloying of the base metals and the brazing material occurs. In welding, in the most common sense, there is one material throughout the base materials and the joining material. A cross section would show a difference in grain structure, but pretty much the same chemical composition. This is desirable to eliminate possible electrochemical differences between the junction elements.

The solder doesn`t know what you are soldering, so such a paste could also be used to solder pipes

Actually, no. Copper is too god a heat conductor and there is too much "cold mass" in a pipe that soldering is out of question. (That is, you cannot transfer enough heat from the soldering iron to the copper mass fast enough for any practical soldering.)

You'd end up using a brazing torch to get enough heat, and by that time you can skip the idea of soldering and switch to real brazing, with all of its advantages.

(To test this out, try to solder together two solid pieces of iron or other metal.)

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